#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

int main(){

	double x1,y1,x2,y2;
	cin >> x1 >> y1 >> x2 >> y2;
	cout << fixed << setprecision(3) << sqrt(pow(x2-x1,2)+pow(y2-y1,2));

    return 0;
}
